instead they want to put them to good use, eventually turning them into renewable energy. this is the demonstration just about an hour ago here outside city hall as workers put a couple dozen trees in to the chipper. crews from the recycling contractor will begin collecting people's old trees starting next week. workers expect in the end to recycle more than 500-tons of trees. the manager said all of those wood chips can be burned. the heat turns the generator and creates power. when you put your old tree out on the curb for pick up make sure to take everything off it. >> if the lights and ornaments still on it we can't put it in the chipper, it'll contaminate the load, ruin the product. if it's not stripped of all those things that will go into the trash and to the landfill. we don't want that. >> reporter: if you live in san francisco, you can pit your tree out on the curb starting next wednesday, january 2nd, put it out onto normal collection day next to the trash bin and the folks will come by and grab it. the program will go for two weeks and there is no charge. >> to